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References: <7997200675c1a53b1954fdc3f46dd208db5dea77.1292578808.git.harald.gustafsson@ericsson.com>
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Date: Fri, 17 Dec 2010 16:54:04 +0100
Message-ID: <AANLkTim3gwwnJmWTbAVRo50JTgHENriJdEPk+v68W8ns@mail.gmail.com>
Subject: Re: [PATCH 1/3] Added runqueue clock normalized with cpufreq
From: Harald Gustafsson <hgu1972@gmail.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
        Harald Gustafsson <harald.gustafsson@ericsson.com>,
        Dario Faggioli <faggioli@gandalf.sssup.it>,
        linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
        Claudio Scordino <claudio@evidence.eu.com>,
        Michael Trimarchi <trimarchi@retis.sssup.it>,
        Fabio Checconi <fabio@gandalf.sssup.it>,
        Tommaso Cucinotta <cucinotta@sssup.it>,
        Juri Lelli <juri.lelli@gmail.com>, Dario Faggioli <raistlin@linux.it>
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2010/12/17 Thomas Gleixner <tglx@linutronix.de>:
> Also if you want to have your deadline scheduler aware of cpu
> frequency changes, then simply limit the total bandwith based on the
> lowest possible frequency and it works always. This whole dynamic
> bandwith expansion is more an academic exercise than a practical
> necessity.

This would severely limit the bandwidth available to deadline tasks. Which
then also reduces the use cases that could benefit from using sched deadline.
Also it would imply a over-reservation of the system, e.g. if you need 10%
BW of the total system and the lowest speed is at 20%, you basically need to
set a BW of 50%, to always be guaranteed that you get your 10% when cpufreq
clocks down. If you use cpufreq and want to use sched deadline this has
strong practical implications and is definitely not academic only.
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